Debit account twice in 2 weeks time

I took out a personal loan with Nedbank. with the signing of the agreement the debit order date was set to the 1st of each month. In the meanwhile Nedbank debits my account when they feel so. ranging from the 22st of the month. After requesting to change the debit order to the 25th of the month when I get paid they go and debit my account now on the 1st again after already deducting on the 22nd of last month. This is really not on Nedbank